Seat belts are used for example in motor vehicles, aircrafts and other mobile devices for restraining the occupant. To perform their function, the seat belts need to have a predetermined tensile strength. Furthermore, the seat belts should generally comprise a surface having as low friction as possible and a soft edge, in order that the occupant is obstructed by the seat belt as little as possible and the clothes of the occupant are not damaged.
The seat belt webbing comprises a plurality of warp threads running in the longitudinal direction which are connected with each other by a weft thread running transversely to the warp threads. During the weaving process, the weft thread is shot through the warp threads from one side of the belt webbing using a weft needle and is caught on the other side using a catch thread, so that when the weft needle is retracted the weft thread is not retracted with it. In the case of loading the seat belt webbing during an accident the warp threads are the load-bearing threads and therefore need to have a certain tensile strength, whereas the weft thread is loaded to a lesser extent and essentially forms the surface of the belt webbing. Thus, the weft thread should have better surface properties than the warp threads, however, in the sense of a softer surface may have a lower tensile strength than the warp threads.
From EP 1 514 962 A2, a belt webbing is known, which in the edge regions comprises warp threads having a different shrinkage characteristic than the warp threads in the central region. In the successive shoots, the weft thread is inter-woven with a varying number of warp threads, so that in the edge region certain warp threads, for example at every fourth or fifth shoot only, are looped around by the weft thread. After weaving the belt webbing it is subjected to a heat treatment, during which a soft edge is formed by intentionally shrinking the warp threads differently in the edge region.
Furthermore, seat belt webbings are known, in which the warp threads in the edge region are designed to be considerably finer than the warp threads in the central region. Owing to the finer warp threads in the edge region, the edge of the seat belt webbing is softer and the surface of the seat belt webbing is considerably more homogeneous, so that the sawing effect of the seat belt webbing when rubbing against the edge is considerably reduced.
It is the object of the invention to provide an enhanced seat belt webbing comprising a soft edge and a method for manufacturing the same.